1. Field of the Invention
This invention is directed to a low sensitivity, energetic plasticizer that is especially useful for explosive and propellant compositions.
2. Description of the Related Art
Energetic materials have found widespread use, perhaps no more extensively than in composite propellants and explosive compositions.
Both solid propellants and explosives are commonly made by preparing a mixture of a finely divided organic or inorganic oxidizing agent, a liquid polymeric binder, a plasticizer as a processing aid, and optionally one or more of the following ingredients: a metallic fuel; an energetic solid fuel or explosive fill; a curative and curing agent; and various modifying agents and other additives. In the case of a solid propellant, ballistic modifiers may also be added. Once prepared, the mixture is cast into a suitable structure, such as a rocket motor case for propellants, then subject to curing, if appropriate, i.e., if a curative and cure catalyst have been included. The polymeric binder acts both as a fuel for reaction with the oxidizing agent and as a binder to provide the cast composition with desired physical properties.
The development of a functionally satisfactory energetic composition useful for explosives and propellant systems requires consideration of an extraordinarily complex combination of characteristics. On the one hand, the compositions usually are expected to pass relatively high performance criteria, even under extreme environments to which such compositions are exposed in normal operations. On the other hand, factors such as processability, safety, environmental impact, and costs must also be considered, often to the detriment of energetic performance. Among the most critical safety issues are thermal stability and detonation insensitivity. Explosive and propellant compositions advantageously should have sufficiently low sensitivities to impact so that accidental detonation or ignition do not occur during handling, storage, and transport of the compositions.
As mentioned above, plasticizers are usually incorporated into energetic compositions as processing aids to improve the workability, flexibility, and/or distensibility of the binder of the composition. These improvements are accomplished by, for example, altering mechanical properties such as glass transition temperature or formulation viscosity. One of the better known and more frequently used plasticizers, BDNPA/F (more formally known as bis(2,2-dinitropropyl)acetal/bis(2,2-dinitropropyl)formal), has found acceptance in the art due to its ability to lower viscosity and improve workability of polymeric compositions. BDNPA/F is also attractive because its synthesis can be conducted in an environmentally friendly manner, as disclosed in U.S. Pat. Nos. 5,648,556 and 5,449,835. However, as in the case of many other plasticizers, BDNPA/F is oxygen deficient, making BDNPA/F relatively low in energy capacity. Also, BDNPA/F has shown good chemical compatibility with only selected binders.
It has long been thought that compromise among these divergent concerns of energetic performance, processability enhancement, and safety could be found by the use of an energetic plasticizer in place of BDNPA/F. One of the best known energetic plasticizers is nitroglycerine, which is well known for its use with nitrocellulose in double-base and triple-base propellants and explosive powders. A significant drawback shared by nitroglycerine and other nitrate ester-containing molecules, and polyolpolynitrates, such as diethyleneglycol-dinitrate (DEGDN) and triethyleneglycol-dinitrate (TEGDN), is their poor thermal stability and high shock sensitivity, which make compositions containing such plasticizers dangerous to handle and extremely prone to accidental detonation. Additionally, preparatory processes are complicated by the need to use NOx scavengers.
Thus, although it has been long recognized that energetic nitrate-containing compounds, such as nitrate esters, exhibit excellent plasticizing properties with a variety of polymeric binders and sufficiently high energetic performances for many propulsive and explosive applications, conventional plasticizers disadvantageously exhibit shock sensitivities and thermal stabilities that are inadequate for many of the environments and the handling which such plasticizers encounter.
It is, therefore, an object of this invention to fulfill the long-felt need in the art outlined above by providing a plasticizer that is at least as energetic as nitrate ester-containing plasticizers, but exhibits far superior shock sensitivity and thermal stability than nitrate ester-containing plasticizers, and in particular nitroglycerine.
In accordance with the principles of this invention, the above and other objects are attained with the use of a novel plasticizer, 2,2-dintrio-1,3-propanediol diformate (also referred to herein as A-diol-diformate or ADDF) having the molecular formula C5H6N2O8 as a chemical structure as follows: 
The present inventors discovered that because the ADDF structure is at least essentially free, if not completely free of nitrate esters, yet contains ester groups, the poor thermal stability and shock sensitivity characteristics associated with conventional nitrate ester plasticizers such as nitroglycerin, DEGDN, and TEGDN, can be overcome without sacrificing energetic properties.
This invention is also directed to explosive and propellant compositions having, as an ingredient, ADDF as a plasticizer.
This invention is further directed to ordnances (or munitions) and rocket motors comprising said explosive and propellant compositions.
This invention is still further directed to a method of making ADDF.
These and other objects, features, and advantages of this invention will be apparent to those skilled in the art upon reading the specification, when taken in conjunction with the accompanying Figure, which explain the principles of this invention.